Chapter30 Aorta

766

Section V: Cardiac Radiology

*

*

1 2

RA

4 3

LA

Figure 30.7.  Subclavian Steal. Coronal MIP CT demonstrates narrowing of the proximal left subclavian artery secondary to large noncalcified atherosclerotic plaque ( arrow ). Normal origins of the vertebral arteries (*) from the ipsilateral subclavian arteries. Patient presented with diminished left upper extremity pulses.

Figure 30.5.  Quadricuspid Aortic Valve. Gradient echo MR image, transverse view of the aortic valve demonstrates the clover-leaf mor- phology of a quadricuspid valve ( arrow ) with four valve leaflets (1–4). LA, left atrium; RA, right atrium.

in subclavian steal syndrome if there is hemodynamically sig- nificant obstruction. Findings on cross-sectional imaging of proximal subclavian narrowing with suggestive clinical his- tory including symptoms of limb ischemia, differential arm pressures, or vertebrobasilar insufficiency should prompt con- cern for subclavian steal syndrome (Fig. 30.7). The aortic isthmus is a physiologic narrowing of the aortic arch between the left subclavian artery origin and ligamentum arteriosum, the embryologic remnant of the ductus arteriosus (Fig. 30.8). Focal prominence of the aorta at the ligamentum arteriosum is a normal variant, termed a “ductus diverticu- lum” or “ductus bump” and should not be confused for an aneurysm or pseudoaneurysm. Distal to the ligamentum arte- riosum, the aorta continues as the descending thoracic aorta

above the pulmonary arteries toward the left (Fig. 30.6). Usually the aortic arch gives rise to three great vessels, occurring in 74% to 80% of the population (Fig. 30.1). The first vessel to branch from the aorta is the right brachioce- phalic or innominate artery which bifurcates into the right common carotid artery and subclavian artery a few centime- ters from its origin. The left common carotid artery and left subclavian artery are the second and third vessels to branch from the aortic arch, respectively. The vertebral arteries normally arise from the proximal aspect of the subclavian arteries. Narrowing of the subcla- vian arteries proximal to the origin of the vertebral arteries, whether degenerative, inflammatory, or iatrogenic, can result

Trachea

Ao

PA

A.Ao

PA

D.Ao

A

B

Figure 30.6.  Normal Ascending Aorta and Left Arch. Axial CT image demonstrates ascending aorta ( A. Ao ) is located slightly posterior and to the right of the main pulmonary artery ( PA ) ( A ). Descending thoracic aorta ( D. Ao ) is to the left of the spine. PA chest radiograph demonstrates a normal left-sided aortic arch to the left of the trachea ( arrow ) and spine, positioned above the main pulmonary artery contour ( B ).